Rear Spring Sag

[DSorenson]

I recently purchased a slide-in camper to use with my 3500 SRW and been struggling the rear suspension. The camper weights ~2,250 lbs which should not be an issue for a 3500. To keep this story somewhat brief, in my quest to stabilize the ride and prevent bottoming out I have added Stabloads, air bags and a sway bar. The sway bar being the most recent addition as of today. While working on the installation I happened to notice for the first time a that the left side was more than an inch lower than the right with both air bags at the same pressure (either inflated or even worse when both were completely deflated). I also have noticed that the Stabloads on the left touch down way before they do on the right and that the left spring simply looks flatter than the right. I have to completely deflate the right air bag and run the left bag up to 70 PSI to get things even close to level.



Has anyone ever had a spring fail?



The truck is a 03 with 85k miles. I have owned it for the past 35k miles (~4 years) and have never heavily loaded the truck or hit anything. The first owner used the truck to pull a 5th wheel.



Thanks in advance for any insight or advice.



Don

 

[jelag]

I have owned 5 of these trucks over the years each towing heavy loads, we've never broken a spring or had one sag... all are gone except for my 05 3500 dually. On this truck, as well as the other trucks in the past we towed 2 axle 22K lb trailers. I don't think the 05 has towed over 3 or 4 tanks of fuel empty... it now tows my 15K lb 5er. We've done 2 things to each of the trucks in the past... we installed a 2x2 tube out of 3/16 wall tube. between the rubber bumper and the frame. . which shortens the stroke before the truck hits the overloads... we also installed pacbrake air bags with a pressure regulator under the hood, which is connected to the air compressor off the pacbrake exhaust brake...

When empty we run the air bags a 10 psi... you should never run any air bag at zero. . when we're loaded we add air to level the the bed. . we found some of the earlier trucks more sensitive to off sided loads and we ran 2 regulators to offset the load.

I can only assume that your camper is that much off sided in the way its built but hopefully my input has given you some insight... we ran most of the trucks for 500K miles before selling them, so we have a good track record of how they worked. .

If your talking about your truck when its unloaded you've got some problem... . none of the trucks I owned over the years were ever that far off when sitting empty... often one side would be 1/4 - 5/8" high or low empty but each of these trucks ran flat beds and extra fuel tanks and a tool box... so we just never worried about them...

And the Dodges towed much better than the Fords with lower cost per mile.

 

[DSorenson]

Thanks for the comments Jim.

I agree that spring failure would be a relatively rare event. I did some more measuring and experimenting with the camper on, partially on (partially resting on its jacks) and completely off. With the camper completely off the suspension evens out almost perfectly. So with a light load both springs are returning to a common initial shape. I suspect that if one of the springs were really damaged this wouldn't be the case. I also suspect that one side of the camper (the side that sags) is 200-300 lb heavier than the other side (the frig, propane bottles, stove top, heater and battery are all on that side). Subsequently I experimented with air bag pressure on the sagging side and found that if I set it in the range of 30-40 PSI and leave the other side low (5 PSI) things level out reasonably well. The air bags have about a 5" diameter contact plate at the top which equals 20 square inches which in turn at 30-40 PSI would apply 600 to 800 lbs of upward force. As I mentioned I can explain away about half of that force as camper imbalance and rest would have to be chalked up to weakened spring.

For now I'm not going to do any other than run a little extra pressure in the one air bag. But, if I ever graduate to a larger camper I may have to replace one spring.

Don

 

[AH64ID]

I wonder if your slide in is heavier than you think. It takes a more than 3K lbs in the bed of my SRW to make it sag to the OEM overloads.

I suggest finding a scale and measuring the weight on each rear wheel, this will tell you if your asymmetrically loaded, or have a spring issue.

 

[DSorenson]

That's a good point. I'll have the truck down in Denver next week and I'll stop at one of the truck-stops that has truck scale.

 

[dieselfreak5.9]

I would weigh the camper left and right separate if you can. You will probably find that the camper weighs more than the sticker and for sure not even. My camper is 700# heavier on the passenger side and I have all the same mods as you. Mine is a Dually and I have to run the right bag at 80# and the left at 20# to even it out. The sticker on the back of my camper says 3900# with all the goodies but it really weighs 5000#. It took me a long time to figure out the right way to load it with gear and loading the camper on the truck to help even things out. My camper base is 1 1/2" narrower than my wheelwells so i made a widget to make sure that the camper bas is tight against the driver side which almost evens the 700# offset out in itself. Also, make sure that you are on a flat and level spot while making adjustments. My driveway is slightly off level and I would get it perfect and then get to a parking lot or gas station and it was way off. Lots of leverage there with the height and weight of the campers. Hope this helps.

 

[DSorenson]

Thanks for the comments and insight into your experience, sounds very much like what I'm seeing! Yeah I kinda suspected that the marketing guys at these truck camper outfits push the engineers aside and get the upper hand when it comes to publishing specs, particularly weight.

I missed my chance to weight the rig this week, but will be driving all next week and I will be sure to find truck scale somewhere and post my results then.